This invention relates to the mould closing, clamping and opening means employed in injection moulding machines, pressure die casting machines and other machines in which a moulding material, such as plastics or metal, is injected at high pressure into a tightly clamped split mould or die, the clamping pressure on which is thereafter released for opening and subsequent ejection of the injection moulded or pressure cast component.
In such machines, one part of the split mould is carried by a fixed front platen, and the other part of the mould is carried by a moving platen which is movable towards and away from the fixed platen to close or open the mould. Means are also required to clamp the parts of the split mould together, when in the closed position, by applying a clamping force to the movable platen.
The mould closing, clamping and opening systems of injection moulding machines at present in use are usually hydraulic in operation and can be divided into four main types:
(1) hydraulic approach jack plus swinging arm and clamping jack, PA1 (2) common hydraulic approach and clamping jack, PA1 (3) toggle approach plus clamping jack, and PA1 (4) toggle approach with over-centre action to create clamping force.
In system (1) a swinging arm is arranged to oscillate about an axis parallel to the line of movement of the moving platen towards and away from the fixed platen of the machine, the oscillating movement being timed to interpose the free end of the arm as a distance piece between the moving platen and a fixed hydraulic clamping jack after the moving platen has been moved to the mould closing position by an approach jack, and to remove the free end of the arm during the mould opening time in the machine cycle. The interposition of the free end of the swinging arm between the hydraulic clamping jack and the moving platen saves energy in that it is not necessary for the hydraulic clamping jack to operate over the complete distance required to open and close the mould.
In system (2) the whole process of closing, clamping and opening the mould is performed by one hydraulic jack but the system suffers the major disadvantage of consuming a considerable amount of energy by virtue of the large amount of oil used to move the moving platen between the open and closed positions of the mould.
System (3) uses a double toggle mechanism, the difference in length between the toggle mechanism when extended and the toggle mechanism when collapsed effectively interposing a distance piece between the moving platen and the hydraulic clamping jack at the end of the mould closing operation, so as to permit mould clamping by the clamping jack.
System (4) is similar in operation to system (3) but uses the over-centring characteristics of toggle mechanisms to provide the final mould clamping force.
These last two systems have the advantage of a relatively high speed of operation, resulting in shorter production cycle times, but possess the disadvantage that rapid wear occurs in the toggle mechanism due to the uneven lubrication inherent in the design. Moreover they are expensive to manufacture. System (4) possesses the additional disadvantage that it fails to maintain constant clamping pressures on the mould due to thermal expansion taking place during a working day. All four systems in addition suffer the further major disadvantage that when one of the tie bars connecting the platens breaks they fail to stop the machine instantly which leads to high stresses being induced in the remaining tie bars. Inevitably this causes these remaining tie bars to fail at a later date.
One of the objects of the present invention is to enable the advantage of the first system to be secured whilst avoiding the disadvantages inherent in all the systems. Another object is to provide mould closing, clamping and opening means which are simple in construction and maintenance, smooth and rapid in operation and conserve energy. A further object of the invention is to provide such means wherein the daylight may readily be adjusted in a simple and convenient manner.